1. Field of the Invention
The present invention relates to a system and method of viewing pairs of perspective images of 3-D objects (i.e. stereoscopic image pairs) displayed from a CRT display surface in a time-multiplexed or field-sequential manner, and more particularly to a universal method of generating control signals for synchronously changing the optical state of liquid crystal (LC) shutter panels through which the time-multiplexed perspective images can be sequentially viewed in a substantially flicker-free manner by the left and right eyes of a human viewer, independent of whether the images are displayed on NTSC, PAL, VGA or SVGA styled CRT display devices.
2. Brief Description of the Prior Art
During the course of human history, man has developed numerous ways of displaying two-dimensional (2-D) images of real and synthetic images alike. In many ways, the evolution of image display technology can be linked to particular stages of development in human civilization.
In the contempory period, diverse types of image display devices have been developed for displaying 2-D images. Examples of such technologies include: cathode ray tube (CRT) display monitors; liquid crystal display panels; plasma display panels; active-matrix plasma display panels; and the like. Presently, the CRT display device (i.e. CRT tube) is widely used in most video monitors of personal computer (PC) systems, as well as in most commercially produced television sets. The principal difference between a CRT computer video monitor and a CRT television display tube is the rate at which image frames or lines are Us are displayed, and the composition of the video signals which each such display device is designed to receive and process during the image display process. In conventional CRT-based television sets, which are constructed and operate according to NTSC or PAL design criteria, the horizontal and vertical synchronization (retrace) signals are multiplexed with the RGB (i.e. color) signals to produce a single composite video signal that is transmitted over a signal conductor, reference to electrical ground. In conventional CRT-based computer display monitors, which are constructed and operated according to VGA or SVGA design criteria, the horizontal synchronization (retrace) signal, the vertical synchronization (retrace) signal, and the RGB (i.e. color) signals are each transmitted over a separate signal conductor, referenced to electrical ground, necessitating a six (6) pin electrical connector for VGA and SVGA styled video monitors. Inasmuch as these design standards create different electrical interface requirements for such types of CRT display devices, NTSC and PAL video display devices can only be driven by NTSC and PAL video signals, respectively, whereas VGA and SVGA styled video display monitor devices can only be driven by VGA and SVGA video signals, respectively. From a practical point of view, VGA or SVGA video signals generated from a graphics accelerator/video board within a computer graphics workstation cannot be used to produce video graphics on a CRT-based television set without the use of special signal conversion equipment. Similarly, composite NTSC or PAL video signals generated from VCR player cannot be used to produce video graphics on a CRT-based computer video monitor without the use of such special signal conversion equipment.
CRT-based display, devices (i.e. computer monitors) designed to be driven by VGA or SVGA video signals typically have an interlace mode and a non-interlace mode (page-flip mode), while CRT-based display devices (I.e. Television sets) designed to be driven by composite NTSC or PAL video signals have only an interlace mode. By virtue of the interlace mode, it is possible for all of the even lines of a video frame to be displayed on the surface of the CRT tube during the first portion of a display period, while all of the odd lines of a video frame are displayed on the surface of the CRT tube during the second portion of a display period, effectively doubling the image display rate at perceived by the eye of the viewer, and thereby reducing image flicker.
Today there is a movement to display stereoscopic image pairs displayed on CRT display devices in order support stereoscopic 3-D vision with full 3-D depth sensation in diverse environments.
While there exist several different techniques for achieving stereoscopic 3-D viewing, the xe2x80x9cfield-sequentialxe2x80x9d or xe2x80x9ctime-multiplexingxe2x80x9d technique enjoys great popularity as it can be easily carried out using a pair of LCD shutter glasses. The function of the LCD shutter glasses is sequentially present to the left eye of a viewer, the left image (of a stereo pair) displayed on a CRT display screen during left image display period, and thereafter, present the right image of the viewer the right image of the stereo pair displayed during right image display period. Over the left and right display periods, the perceived left and right images fuse to provide stereopsis in the mind of the viewer.
The function of the LCD shutters is to sequentially undergo a change in optical state during the left and right image display periods, to allow the viewer stereoscopically view sequentially displayed stereoscopic pairs. This function is carried out by electrically switching the optical state of the LCD shutters in response to trigger signals produced from the video signals. In particular, at the beginning of the left image display period, the optical state of the left eye LCD shutter is synchronously switched from its opaque state to its transparent state and the optical state of the right eye LCD shutter is synchronously switched from its transparent state to its opaque state. Then at the beginning of the right image display period, the optical state of the right eye LCD shutter is synchronously changed from its opaque state to its transparent state and the optical state of the left eye LCD shutter is synchronously changed from its transparent state to its opaque state. Such synchronously switching operations require the generation of trigger (i.e. switching) signals for driving the operations of the LCD shutters.
Presently, a number of LC shutter glasses are commercially available for use with the field-sequential stereoscopic 3-D image display technique. While some LCD shutter glasses are designed for use with CRT display devices driven by VGA video signals (i.e. computer monitors), others are designed for use with CRT display devices driven by composite video sources (e.g. television sets). However, there does not exist a pair of LCD shutter glasses that can be used with either type of CRT display device.
Prior art LC shutter glasses suffer from a number of shortcomings and drawbacks. In particular, many prior art LC shutter glasses attempt to synchronize the shutter transition to the beginning of each video frame. Once a vertical reset pulse or similar signal is detected, pulse coded information is sent to toggle the optical state of the shutters. However, as this information is sent at the beginning of each field of video, it must be of very short duration in order to allow sufficient time for the shutters to change state before the vertical blanking interval ends. This prior art shutter-state control/synchronization technique requires providing high speed circuitry in the LC eyewear (or associated receiving unit) in order to decode these short time-domain shutter control pulses. Moreover, such circuitry utilizes battery power, and thus shortens the effective life of the batteries aboard the electro-optical shutter glasses.
Another shortcoming of prior art shutter glasses is that a background excitation voltage is required to keep the pi-cell shutters in the transmissive state.
Thus there is a great need in the art for an improved stereoscopic viewing system which avoids the shortcomings and drawbacks associated with prior art systems and methodologies.
A primary object of the present invention is to provide a stereoscopic 3-D image viewing system for stereoscopically viewing 3-D images displayed on either a CRT computer or video display device.
Another object of the present invention is to provide such a system, in which lightweight stereoscopic 3-D shutter-type viewing glasses are used to view stereoscopic image pairs displayed on a CRT computer or video display device according the time-multiplexing display technique.
Another object of the present invention is to provide such a system, in which signal decoding and processing is minimized within the stereoscopic 3-D shutter-type viewing glasses in order to reduce the cost of manufacture thereof, while providing extended battery life.
Another object of the present invention is to provide a pair of LCD shutter glasses having a passive mode of operation for use in decoding micropolarized spatially-multiplexed images displayed from an spatially-multiplexed image display system.
Another object of the present invention is to provide such a system, in which a means is provided for detecting stereoscopically encoded video synchronization signals from a computer or other video source and transmitting field information for controlling remote pairs of optical state varying LCD shutters via pulse width modulated infrared. pulses.
Another object of the present invention is to provide such a system, in which one shutter switches to the transmissive state while the other shutter switches to the opaque state synchronized to a specific field of information displayed on the CRT or display device.
Another object of the present invention is to provide a stereoscopic viewing system, which has a display mode that allows two viewers, wearing two separate pairs of LCD glasses of the present invention to view two separate images simultaneously on the same display screen. for example, to play a head-to-head video game on the same viewing screen without interference.
Another object of the present invention is to provide a stereoscopic viewing system, wherein the polarization axis of the LCD shutters glasses can be passively oriented in opposing directions and thus be used as a pair of electrically-passive polarizing glasses to stereoscopically view spatially multiplexed images (SMI).
Another object of the present invention is to provide a stereoscopic viewing system, having several different modes of operation which make it possible for a viewer, in a multi-format stereoscopic environment, to view a variety of stereoscopic images with the same viewing glasses.
Another object of the present invention is to provide a method of generating synchronization signals for use in a stereoscopic viewing system which employs low cost, twisted nematic (TN) liquid crystal (LC) displays as the optical shutters, and control signals adjusted for the slower transition times and inherent process variations associated therewith.
Another object of the present invention is to provide a synchronization signal generation scheme which has the inherent ability to detect interlaced and non-interlaced modes in computer generated or standard video signals, and transmit appropriate shutter control signals via an infrared link to the remote shutter glasses.
Another object of the present invention is to provide such a synchronization signal generation system, in which the synchronization control signals generated therefrom are adjustable for the slower transition times and inherent process variations associated with optical shutters constructed from low-cost twisted nematic (TN) liquid crystal (LC) display panels which do not require any background excitation voltage while in the clear state, and thus longer battery life can be achieved.
Another object of the present invention is to provide a pair of LC optical shutter glasses constructed from low-cost twisted nematic (TN) liquid crystal (LC) display panels which do not require any background excitation voltage while in the clear state, and thus longer battery life can be achieved.
Another object of the present invention is to provide a pair of LC optical shutter glasses, in which the shutter drive circuitry is effectively disposed into a xe2x80x9csleepxe2x80x9d mode until a change of optical state is required by the shutter panels, thereby substantially increasing battery life.
Another object of the present invention is to provide a novel shutter-based stereoscopic viewing system, having a synchronization signal transmitter with a multi-synch detection capability for interpreting both interlaced and non-interlaced video conditions, generating synchronization signals and transmitting the same to optical shutters glasses for controlling the optical state of the same.
Another object of the present invention is to provide a universal multi-sync signal detection device that can detect synchronization signals, polarities and frequencies present in all VGA and SVGA video formats, as well as, NTSC and PAL composite video sources; determine the image field rate from these signals; determine the presence or absence of stereoscopically encoded video signals; and transmit the appropriate signals for controlling the optical shutters in the remote viewing glasses.
Another object of the present invention is to provide a shutter glasses with decoding circuitry that detects the presence of pulse width modulated infrared signals, recognize a difference between two adjacent pulses and sets the corresponding optical shutter state.
Another object of the present invention is to provide shutter glasses with decoding circuitry which, when detecting no difference between two adjacent IR pulses, automatically determines that a non-interlaced video condition exists and places both optical shutters in the optically transmissive state indicating a non-stereoscopic video image is to be viewed.
Another object of the present invention is to provide shutter glasses with decoding circuitry which, when detecting alternating pulse widths of two predetermined lengths, automatically determines that an interlace condition exists, and simultaneously alters the optical state of the LCD shutters at the corresponding video field rates for viewing stereoscopic video images.
Another object of the present invention is to provide shutter glasses with decoding circuitry which, when detecting no IR pulses automatically enters a sleep mode or off sleep-state which will place both optical shutters in the optically transmissive state.
Another object of the present invention is to provide shutter glasses which do not require any background excitation voltage to keep the shutters in the optically transmissive state.
Another object of the present invention is to provide such shutter glasses, in which the polarization state of the optical-state varying shutters are oriented orthogonally when operated in their electrically-passive transmissive state, for use in stereoscopically viewing linearly polarized spatial multiplexed images.
Another object of the present invention is to provide a stereoscopic 3-D image viewing system based on the spatially-multiplexed image (SMI) display form, in which the shutter glasses of the present invention are used in their electrically-passive transmissive state, for stereoscopically viewing linearly micropolarized polarized SMIs displayed from an LCD panel.
These and other object of the present invention will become apparent hereinafter.